Author

Degree

Program

Supervisor(s)

Prof. Jeffrey L. Hutter

Abstract

The process of crystal growth has been intensively studied, for both its academic interest and industrial importance. I report here two studies of crystal growth.

The normal alkanes are an interesting, both in terms of their intrinsic properties and because many biological materials contain hydrocarbon domains. The normal alkanes often exhibit complicated phase behaviour, with phase diagrams containing multiple solid phases. We report here a curious pattern of twinned domains seen in one phase of tricosane (C23H48), which we have studied by X-ray diffraction, as well as by optical and atomic force microscopy. This pattern is seen in the rotator RV phase, a monoclinic arrangement of tricosane molecules without orientational order. Transitions between this polymorph and the orthorhombic phase lying at higher temperatures preserve features at the molecular level, and thus represent a diffusionless, martensitic-like transformation.

Calcium oxalate monohydrate (COM) is the primary constituent of most kidney stones. Certain proteins, such as osteopontin (OPN), inhibit stone formation. The inhibition of crystallization due to adsorbed impurities is usually explained in terms of a model proposed in 1958 by Cabrera and Vermilyea, which hypothesizes that impurities adsorb to growth faces and pin growth steps, thus impeding their progress via the Gibbs-Thomson effect. To determine the role of OPN in the biomineralization of kidney stones, crystal growth on the {010} face of COM was examined in real time by atomic force microscopy in the presence of a synthetic peptide. We observed clear changes in the morphology of the growth-step structure and a decrease in step velocity upon addition of inhibitors, suggesting adsorption on the {010} growth hillocks. Experiments in which inhibitors were replaced in the growth cell by a supersaturated solution showed that COM hillocks are able to fully recover to their pre-inhibited state. Our results suggest that recovery occurs through incorporation of the peptide into the growing crystal, rather than by, e.g., desorption from the growth face. This work provides new insights into the mechanism by which crystal growth is inhibited, with important implications for the design of therapeutic agents for kidney stone disease and other forms of pathological calcification.